It is well known from photoacoustic theory (A. Rosencwaig and A. Gersho, J. Appl. Phys. 47, 64 (1976) and A. Rosencwaig, Photoacoustics and Photoacoustic Spectroscopy, Wiley, Interscience, New York, 1980) that one can, with thermal waves, obtain information about the thermal characteristics of a sample as a function of depth beneath its surface. Thermal characteristics or features are those regions of an otherwise homogeneous material that exhibit variations relative to their surroundings in thermal conductivity, thermal expansion coefficient or volume specific heat. Variations in these thermal parameters can arise from changes in basic material composition or from the presence of mechanical defects such cracks, voids and delaminations. Variations in thermal parameters can also arise from changes in the crystalline order or structure or due to the presence of small concentrations of foreign ions or lattice defects in an otherwise perfect crystal. Although there has been some experimentation in thermal-wave depth-profiling, (M. J. Adams and G. F. Kirkbright, Analyst 102, 678 (1977)) and A. Rosencwaig, J. Appl. Phys. 49, 2905 (1978) this capability has not been extensively exploited, primarily because of the lack of adequate theoretical models. A recent model of Opsal and Rosencwaig, (J. Opsal and A. Rosencwaig, J. Appl. Phys. 53,4240 (1982)) (O-R model) shows how depth-profiling and multi-layer thickness analysis can be performed from thermal-wave measurements using either surface temperature or thermoacoustic probes, and allows for a fuller exploitation of this depth-profiling capability. There have also been several experimental impediments to thermal-wave profiling. For example, one would like, in many cases to operate outside of a photoacoustic cell, to employ a completely contactless method for thermal-wave generation and detection, and to couple thickness measurements with high spatial resolution, this last requirement necessitating the use of high-frequency (&gt;100kHz) thermal waves.